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Chapter 2-Conference Profiles
Polycom, Inc. 2-9
AVC Conferencing Parameters
When defining a new video Profile, you select the parameters that determine the video
display on the participant’s endpoint and the quality of the video. When defining a new
conference Profile, the system uses default values for Continuous Presence (CP) standard
conferencing. Continuous Presence conferencing enables several participants to be viewed
simultaneously and each connected endpoint uses its highest video, audio and data
capabilities up to the maximum line rate set for the conference.
Basic Conferencing Parameters
The main parameters that define the quality of a video conference are:
• Line (Bit) Rate - The transfer rate of video and audio streams. The higher the line (bit)
rate, the better the video quality.
• Audio Algorithm - The audio compression algorithm determines the quality of the
conference audio.
• Video protocol, video format, frame rate, annexes, and interlaced video mode - These
parameters define the quality of the video images. The Collaboration Server will send
video at the best possible resolution supported by endpoints regardless of the
resolution received from the endpoints.
— When Sharpness is selected as the Video Quality setting in the Conference Profile, the
Collaboration Server will send 4CIF (H.263) at 15fps instead of CIF (H.264) at 30fps.
— H.264 High Profile protocol provides better compression of video images in line
rates lower than 384 Kbps and it will be automatically selected for the endpoint if it
supports H.264 High Profile. If the endpoint does not support H.264 High Profile,
the Collaboration Server will try H.264 Base Profile which provides good
compression of video images in line rates lower than 384 Kbps (better than H.263
and not as good as H.264 High Profile).
— When working with Collaboration Servers at low bit rates (128, 256, or 384Kbps),
HDX endpoints will transmit SD15 resolution instead of 2CIF resolution.
When using a full screen (1x1) conference layout, the Collaboration Server transmits the
same resolution it receives from the endpoint.
• Supported resolutions:
— H.261 CIF/QCIF – Is supported in Continuous Presence (CP) conferences at
resolutions of 288 x 352 pixels (CIF) and 144 x 176 pixels (QCIF). Both resolutions
are supported at frame rates of up to 30 frames per second.
— H.263 4CIF - A high video resolution available to H.263 endpoints that do not
support H.264. It is only supported for conferences in which the video quality is set
to sharpness and for lines rates of 384kbps to 1920kbps.
2560
Video Switching
3072
3584
4096
6144 Not Supported Video Switching
Table 2-4 Video Session Mode by Line Rate and Card type (Continued)
Line Rate (kbps) MPM MPM+ MPMx